Interesting number

input/code.cpp: In function 'int main()':
input/code.cpp:29:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int j = 0; j < is.length()/2; j++){
                                    ^

#include <bits/stdc++.h>

using namespace std;

string ints(int n){
  stringstream ss;
  ss << n;
  return ss.str();
}  
int main(){
  cin.sync_with_stdio(0);
  cin.tie(0);
  int tests; cin >> tests;
  int prim[1010] = {0};
  for(int i = 3; i <= 1000; i+=2){
      bool g = true;
      for(int j = 2; j < i ; j++){
	  if(i%j == 0){
	    g = false;
	    break;
	  }
      }
      prim[i] = g;
  }
  map<string, bool> pal;
  for(int i = 1; i <= 1000; i++){
    string is = ints(i);
    bool g = true;
    for(int j = 0; j < is.length()/2; j++){
	if(is[j] != is[is.length()-1-j])
	  g = false;
    }
    pal[is] = g;
  }
  while(tests--){
      int n; cin >> n;
      int a[1010];
      for(int i = 0; i < n; i++){
	cin >> a[i];
	
      }
      for(int i = 0; i < n; i++){
	if(prim[a[i]] && pal[ints(a[i])]){
	    cout << a[i] << endl;
	    break;
	}
      }
	
  }
  return 0;
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: RUNTIME ERROR